The invention relates to an apparatus and a method for stroke transmission between a drive element and a stroke or reciprocating element.
A stroke transmission is often used in areas where it may be advantageous to separate a drive system into a separate drive element and stroke element. For example, this may be done to simplify a manufacturing process, to permit use of different materials in different parts of the drive system, or to simply provide a change of stroke or ratio.
In the stroke transmission, a particular ratio is set between the secondary stroke (xs) of the stroke element and the primary stroke (xp) of the drive element, expressed by the stroke factor (II), where II=xs/xp.
A stroke gear reduction, corresponding to a stroke factor II less than 1, is realized for example in systems in which a comparatively large-stroke motor is supposed to drive a stroke element having a small travel.
A neutral stroke transmission, corresponding to a stroke factor II=1, is for example desirable if the stroke of an actuator is supposed to be communicated precisely via a stroke element that is realized differently in terms of materials.
A stroke gearing up or multiplication occurs when there is a stroke factor II greater than 1, for example given small-stroke actuators whose stroke is supposed to be enlarged via a stroke element for the necessary application.
For stroke transmission, in particular for stroke gearing up, German patent documents DE 195 19 191 A1 and DE 43 06 072 C2 disclose the use of a hydraulic chamber between the drive element and the stroke element is known, whereby the ratio of the surface of the pressure-exposed drive element to the surface of the pressure-exposed stroke element directly determines the stroke factor.
A problem in stroke transmission is that a combination of different types of stroke transmission is often required. A neutral stroke transmission is often needed at the beginning of an actuation process with a subsequent stroke gearing up, e.g., given a stroke transmission from a piezoelectric actuator to an injector needle or vale needle for the operation of a servo-valve-controlled fuel injector.
In this context, a large force has to be applied for the initial precise opening of a servo-valve chamber. Immediately after this application of force, the pressure in the valve chamber falls to a low value, so that a significantly smaller force is sufficient of the further opening. For the reproducibility of the opening behavior within narrow tolerances (injection quantity, beginning of injection), a wide opening of the valve chamber is required. Due to the small useful stroke of the piezoactuator, a stroke gearing up is necessary for this purpose.
A stroke transmission apparatus and a stroke transmission method are not known wherein a stroke factor II is dependent on a primary stroke xp of a drive element.
One object of the present invention is to provide a stroke transmission capable of providing a variable stroke factor II. Another object of the present invention is to provide a stroke transmission method capable of providing a variable stroke factor II.
These and other objects, features and advantages of the present invention are achieved by a stroke transmission apparatus and a method of transmitting stroke.
For this purpose, a displaceable drive element, a stroke element that can be displaced in the same direction, and at least one lever are used.
Unless otherwise indicated, for better understanding xe2x80x9ca leverxe2x80x9d is to be understood as referring to at least one lever, while the singular is expressed by xe2x80x9cexactly one lever.xe2x80x9d
The lever is applied continuously to the drive element, and can be placed on or in contact with the stroke element and a bearing. The primary stroke xp in which the lever is actually placed on the stroke element and the bearing depends on the respective specific embodiment and on the primary stroke xp.
However, if a simultaneous seating or contact of the lever on the stroke element, the drive element, and the bearing is present, a lever effect results, so that the primary stroke xp of the drive element can be transmitted to the stroke element via the lever action of the lever. The stroke factor II can thereby vary between a gearing up transmission ( less than 1), a neutral transmission (=1) or a gear reduction transmission ( greater than 1).
When the lever effect is present, a primary drive force is transmitted from the drive element to the lever via a force introduction point, and from the lever it is transmitted to the stroke element via a stroke point. The lever is supported on the bearing at a pivot point. The region on the one side of the lever between pivot point and force introduction point thus corresponds to a power arm of length L1, and the region between the stroke point and pivot point corresponds to a work arm of length L1+L2, which is also designated the effective lever length.
In addition, the stroke transmission is formed in such a way that as the primary stroke xp changes, the stroke factor II can be modified at least once by modifying at least one contact point. A contact point is to be understood as a pivot point, a stroke point or a force introduction point.
Such a mechanical stroke transmission has the advantage that, in contrast to a hydraulic or mechanical-hydraulic stroke transmission, the need for a fluid chamber can be eliminated. In this way one advantageous result is that the secondary stroke xs is largely independent of the duration of actuation.
In addition, another advantageous result is that of a stroke transmission free of delay.
A very flexible geometrical construction of the individual components is also advantageously possible, so that the stroke factor II can be varied within a wide range and dynamically. Thus, dependent on the primary stroke xp, it can be varied continuously or discontinuously. The stroke factor II can for example be set to increase, to be constant, to decrease, or to include any combination of these.
For the simple adjustment of the stroke factor II, it is advantageous if the lever is respectively applied continuously to a pivot point on the bearing. In the initial position, i.e. given a primary stroke xp=0,the stroke element is placed loosely on the drive element, and there is a spacing (h) or gap between the lever and the stroke element.
Given an actuation by means of an increase of the primary stroke xp, the spacing h is reduced until the lever rests at a changeover point xp=xt when h=0 on the stroke element. At this point, a lever effect of the lever can be transmitted to the stroke element. In this case, the modification of a contact point thus corresponds to the seating of the lever on the stroke element.
If the primary stroke xp is even smaller than or is equal to the changeover point (xt), i.e. xp xe2x89xa6xt, then the stroke factor II=1, dye to the direct mechanical contact between the drive element and the stroke element. In contrast, it is also generally true that the stroke factor II greater than 1 for xp greater than xt.
For the simple construction, in particular given use in a servo-valve-controlled duel injector, for xp greater than xt a stroke factor II between 1 (e.g., initial opening of the servovalve with large force) to 10 (e.g. wide subsequent application of force) is preferred.
For simpler adjustment, it can be advantageous in the initial position to place the lever on the stroke element and not on the bearing, so that a spacing results between the lever and the bearing. The manner of action of such a construction is analogous to that with a spacing between the lever and the stroke element. For example, if xp is less than or equal to xt, then the stroke factor II is again equal to 1 because the drive element and stroke element are in direct mechanical contact.
For the variable adjustment of the stroke factor II, it is advantageous if the lever sits permanently on the stroke element and on bearing, so that a mechanical non-positive, or frictional, or a surface to surface connection is present between the drive element and the stroke element during the entire stroke process. This is equivalent to a continuous presence of the lever effect. This is caused by the direct contact between the drive element and the lever as well as the direct contact between the bearing and the lever and the stroke element and the lever.
For this purpose, in the initial position each lever is applied to the drive element via a respective interior force introduction point or the contact point.
In the initial position, when xp=0 a direct mechanical contact can additionally be given between drive element and stroke element.
Given a changing primary stroke xp, the lever can be moved in such a way that the respective force introduction point can be modified. By modifying the force introduction point, the stroke factor II can in turn be modified.
The stroke factor II can thereby change at least from one region to the next within a stroke interval of the primary stroke xp, but is can also remain constant from one region to the next. Region utilized herein, unless more specifically identified, refers generally to the surface areas of the elements near the contact points.
For the rapid modification of the stroke factor II, it is advantageous if the external force introduction points, i.e., all force introduction points other than the one for xp=0, are spatially separated from one another. In this way, a discontinuous modification of the stroke factor II can be achieved, given continuous modification of the primary stroke xp.
for the versatile adjustment of the stroke factor II, it is advantageous if the interior and exterior force introduction points are arranged in continuous fashion at least from one region to the next, i.e., passing over into one another spatially. In this way, it is possible to vary the stroke factor II continuously given continuous modification of the primary stroke xp.
For the purpose, it is advantageous if the lever is applied respectively to a surface of the drive element that is curved at least from one region to the next, so that a continuous modification of the stroke factor II can be set, at least from one region to the next, by means of the primary stroke xp. This can advantageously take place in that the surface is alternately curved in convex and in concave fashion, so that the stroke factor II can be modified continuously between continuous surface variations, and can in addition vary between the values  less than 1, =1 and  greater than 1.
In addition, for precise stroke transmission it is advantageous if exactly one lever is present, because by this means an expensive adjustment (e.g. caused by manufacturing tolerances) of the position of several levers can be avoided.
It is advantageous if a primary stroke xp of 10 xcexcm to 100 xcexcm can be executed. This is typically the case if the drive element is driven by a piezoactuator or a magnetic or electronic element. Here the use of a ceramic multilayer piezoactuator is particularly preferred.
The use of a stroke gearing-up device is particularly advantageous in a fuel injector, due to the delay-free switching that can be accomplished by the stroke transmission of the invention.